Error : Failed to start subscriber for topic name /pose and message type std_msgs/Int32.【MATLAB Unity communication】

I’m trying to do Unity MATLAB connection by using ROS.

(reference : https://jp.mathworks.com/help/robotics/ug/pick-and-place-workflow-in-unity-3d-using-ros.html)

I was able to communicate well with the PoseMsg structure, but not with others.

PoseMsg：https://github.com/Unity-Technologies/ROS-TCP-Connector/blob/main/com.unity.robotics.ros-tcp-connector/Runtime/Messages/Geometry/msg/PoseMsg.cs

Int32Msg (For example)：https://github.com/Unity-Technologies/ROS-TCP-Connector/blob/main/com.unity.robotics.ros-tcp-connector/Runtime/Messages/Std/msg/Int32Msg.cs

*******************************************************

I got an error when I run this script at MATLAB.

poseSub = rossubscriber('pose', 'DataFormat', 'struct')

Error message is below

Warning: Error occurred while shutting down the ROS subscriber.

Caused by:
Subscriber 2039 already stopped. 
> In ros/Subscriber/delete (line 361)
In ros.Subscriber (line 216)
In rossubscriber (line 103) 
Warning: Error occurred while removing the ROS subscriber.

Caused by:
Subscriber still active: 2039 
> In ros/Subscriber/delete (line 368)
In ros.Subscriber (line 216)
In rossubscriber (line 103) 
Failed to start subscriber for topic name /pose and message type std_msgs/Int32.

On the other hand, Unity C# script is below

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.Robotics.ROSTCPConnector;
using RosMessageTypes.Geometry;
using RosMessageTypes.Std;
using System;


public class RosPublisher : MonoBehaviour
{
    ROSConnection ros;
    public string topicName = "pose";
    public GameObject obj;
    public float publishMessagePeriod = 0.5f;
    private float timeElapsed;
    // Start is called before the first frame update
    void Start()
    {
        ros = ROSConnection.GetOrCreateInstance();
        ros.RegisterPublisher<Int32Msg>(topicName);
    }

    // Update is called once per frame
    private void Update()
    {
        timeElapsed += Time.deltaTime;

        if (timeElapsed > publishMessagePeriod)
        {
            Int32Msg pose = new Int32Msg(100);

            // Finally send the message to server_endpoint.py running in ROS
            ros.Publish(topicName, pose);

            timeElapsed = 0;
        }
    }
}

[Hari Krishna Kakarla]

Hi MAKOTO,

Thanks for reaching out to us. I see that you are publishing a message of type std_msgs/Int32Msg but you are using topic name as /pose which is little confusing.

What I suspect is, you might be using the same topic for geometry_msgs/PoseMsg as well and the publiser of it is already running? May be that's why it is working for you for the PoseMsg and not for the others.

I am just assuming this by looking at your C# script. Your logic looks correct but topic name and object name is confusing. Please give some other topic name for this msg type Int32Msg and change the object name in the C# script as well. That should solve the problem.

If you are still getting the same error, please give me some more information, i.e. please share the C# scripts of your PoseMsg and Int32Msg and let me know what are all the things you are executing in Unity.

Thanks

Hari

[MAKOTO]

Thanks for your reply.

I redid the ros run and it worked.

Sorry for the trouble.